Valimai follows ACP Arjun Kumar IPS, a Madurai police officer who arrives in Chennai on a mission to pursue a group of violent motorcyclists. This is a crucial case involving a gang of deadly motorcyclists known as the Slave of Satan. Naren aka Wolfrang is a gang leader who runs a notorious business. Arjun finds a ruthless gang with the help of his team and Sophia, Arjuna's friend and partner.

The gang involved in ruthless theft and murder goes berserk as their control over the city widens. How Arjun manages to track down the group and whether he can save a troubled city from a gang of motorcyclists is the rest of the story.